[PATCH] ARM: arch_timer: Silence debug preempt warnings

[PATCH] ARM: arch_timer: Silence debug preempt warnings

[Stephen Boyd]

Hot-plugging with CONFIG_DEBUG_PREEMPT=y on a device with arm
architected timers causes a slew of "using smp_processor_id() in
preemptible" warnings:

  BUG: using smp_processor_id() in preemptible [00000000] code: sh/111
  caller is arch_timer_cpu_notify+0x14/0xc8

This happens because sometimes the cpu notifier, arch_timer_cpu_notify(),
is called in preemptible context but we use this_cpu_ptr()
to retrieve the clockevent unconditionally. We're only going to
actually use the pointer in non-preemptible context though,
so use __this_cpu_ptr() instead to avoid the preemptible checks
and silence the warning.

Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Marc Zyngier <Marc.Zyngier@arm.com>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>
---
 drivers/clocksource/arm_arch_timer.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/clocksource/arm_arch_timer.c b/drivers/clocksource/arm_arch_timer.c
index d7ad425..5928c29 100644
--- a/drivers/clocksource/arm_arch_timer.c
+++ b/drivers/clocksource/arm_arch_timer.c
@@ -248,7 +248,7 @@ static void __cpuinit arch_timer_stop(struct clock_event_device *clk)
 static int __cpuinit arch_timer_cpu_notify(struct notifier_block *self,
 					   unsigned long action, void *hcpu)
 {
-	struct clock_event_device *evt = this_cpu_ptr(arch_timer_evt);
+	struct clock_event_device *evt = __this_cpu_ptr(arch_timer_evt);
 
 	switch (action & ~CPU_TASKS_FROZEN) {
 	case CPU_STARTING:
-- 
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
hosted by The Linux Foundation

[PATCH] ARM: arch_timer: Silence debug preempt warnings

[Stephen Boyd]

On 4/2/2013 1:31 PM, Stephen Boyd wrote:
> Hot-plugging with CONFIG_DEBUG_PREEMPT=y on a device with arm
> architected timers causes a slew of "using smp_processor_id() in
> preemptible" warnings:
>
>   BUG: using smp_processor_id() in preemptible [00000000] code: sh/111
>   caller is arch_timer_cpu_notify+0x14/0xc8
>
> This happens because sometimes the cpu notifier, arch_timer_cpu_notify(),
> is called in preemptible context but we use this_cpu_ptr()
> to retrieve the clockevent unconditionally. We're only going to
> actually use the pointer in non-preemptible context though,
> so use __this_cpu_ptr() instead to avoid the preemptible checks
> and silence the warning.
>
> Cc: Mark Rutland <mark.rutland@arm.com>
> Cc: Marc Zyngier <Marc.Zyngier@arm.com>
> Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>
> ---

Anyone else seeing this one?

>  drivers/clocksource/arm_arch_timer.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/clocksource/arm_arch_timer.c b/drivers/clocksource/arm_arch_timer.c
> index d7ad425..5928c29 100644
> --- a/drivers/clocksource/arm_arch_timer.c
> +++ b/drivers/clocksource/arm_arch_timer.c
> @@ -248,7 +248,7 @@ static void __cpuinit arch_timer_stop(struct clock_event_device *clk)
>  static int __cpuinit arch_timer_cpu_notify(struct notifier_block *self,
>  					   unsigned long action, void *hcpu)
>  {
> -	struct clock_event_device *evt = this_cpu_ptr(arch_timer_evt);
> +	struct clock_event_device *evt = __this_cpu_ptr(arch_timer_evt);
>  
>  	switch (action & ~CPU_TASKS_FROZEN) {
>  	case CPU_STARTING:

-- 
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum,
hosted by The Linux Foundation

[PATCH] ARM: arch_timer: Silence debug preempt warnings

[Marc Zyngier]

Hi Stephen,

On 05/04/13 06:11, Stephen Boyd wrote:
> On 4/2/2013 1:31 PM, Stephen Boyd wrote:
>> Hot-plugging with CONFIG_DEBUG_PREEMPT=y on a device with arm
>> architected timers causes a slew of "using smp_processor_id() in
>> preemptible" warnings:
>>
>>   BUG: using smp_processor_id() in preemptible [00000000] code: sh/111
>>   caller is arch_timer_cpu_notify+0x14/0xc8
>>
>> This happens because sometimes the cpu notifier, arch_timer_cpu_notify(),
>> is called in preemptible context but we use this_cpu_ptr()
>> to retrieve the clockevent unconditionally. We're only going to
>> actually use the pointer in non-preemptible context though,
>> so use __this_cpu_ptr() instead to avoid the preemptible checks
>> and silence the warning.
>>
>> Cc: Mark Rutland <mark.rutland@arm.com>
>> Cc: Marc Zyngier <Marc.Zyngier@arm.com>
>> Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>
>> ---
> 
> Anyone else seeing this one?

Haven't seen this one occurring yet. I suspect my compiler is optimizing
the code in ways that prevent the breakage from being seen.

> 
>>  drivers/clocksource/arm_arch_timer.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/clocksource/arm_arch_timer.c b/drivers/clocksource/arm_arch_timer.c
>> index d7ad425..5928c29 100644
>> --- a/drivers/clocksource/arm_arch_timer.c
>> +++ b/drivers/clocksource/arm_arch_timer.c
>> @@ -248,7 +248,7 @@ static void __cpuinit arch_timer_stop(struct clock_event_device *clk)
>>  static int __cpuinit arch_timer_cpu_notify(struct notifier_block *self,
>>  					   unsigned long action, void *hcpu)
>>  {
>> -	struct clock_event_device *evt = this_cpu_ptr(arch_timer_evt);
>> +	struct clock_event_device *evt = __this_cpu_ptr(arch_timer_evt);
>>  
>>  	switch (action & ~CPU_TASKS_FROZEN) {
>>  	case CPU_STARTING:

I'm afraid this would hide bugs if we start using the notifier for other
purposes than exclusivity non-preemptible contexts.

How about moving the this_cpu_ptr() down to the cases themselves, maybe
with a nice comment?

Cheers,

	M.
-- 
Jazz is not dead. It just smells funny...

[PATCH] ARM: arch_timer: Silence debug preempt warnings

[Stephen Boyd]

On 04/05/13 03:04, Marc Zyngier wrote:
>
>>>  drivers/clocksource/arm_arch_timer.c | 2 +-
>>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/clocksource/arm_arch_timer.c b/drivers/clocksource/arm_arch_timer.c
>>> index d7ad425..5928c29 100644
>>> --- a/drivers/clocksource/arm_arch_timer.c
>>> +++ b/drivers/clocksource/arm_arch_timer.c
>>> @@ -248,7 +248,7 @@ static void __cpuinit arch_timer_stop(struct clock_event_device *clk)
>>>  static int __cpuinit arch_timer_cpu_notify(struct notifier_block *self,
>>>  					   unsigned long action, void *hcpu)
>>>  {
>>> -	struct clock_event_device *evt = this_cpu_ptr(arch_timer_evt);
>>> +	struct clock_event_device *evt = __this_cpu_ptr(arch_timer_evt);
>>>  
>>>  	switch (action & ~CPU_TASKS_FROZEN) {
>>>  	case CPU_STARTING:
> I'm afraid this would hide bugs if we start using the notifier for other
> purposes than exclusivity non-preemptible contexts.
>
> How about moving the this_cpu_ptr() down to the cases themselves, maybe
> with a nice comment?

Ok. v2 coming up.

-- 
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum,
hosted by The Linux Foundation